I am sort of having the same concern about this as with the other stuff:
Sure that one dies but will it be stunned/die fast enough to not release tons more planula into the tank before it's demise?
I've treated a few (just had a few) in my tank and the big ones did die. But now I have tons of babies cropping up in the substrate. NOT cool.

So whatever I use to get rid of it next will have to kill or stun on contact before any babies are released

Reading the instructions on this thing where you have to prod it several times - that doesn't seem like instant kill to me...